To this point, over 70 patients (most with melanoma and including a dozen with objective clinical responses) have had serum and peripheral blood mononuclear cells (PBMC) collected during their initial therapy with IL-2. Over 30 immune related proteins have been interrogated in pretreatment sera by multiplex assay. The pre-treatment PBMC and the PBMC rebound occuring after stopping IL2 have been subjected to Affymetics array analysis which is still in process. Finding molecular factors associated with one of the only curative therapies for melanoma and renal cancer would not only allow treatment to focus on those most likely to benefit, but it could also provide clues to the mechanism by which IL-2 is working.